Automated allocation using spare IP addresses pools

ABSTRACT

Techniques and solutions are provided for performing automated allocation of Internet Protocol (IP) addresses. For example, automated allocation of IP addresses can be performed by determining that remaining IP addresses in an available IP address pool are below a threshold value, obtaining a range of contiguous IP addresses from a common spare IP address pool, and allocating the range of contiguous IP addresses from the common spare IP address pool to the available IP address pool. The available IP address pool can then be used to allocate IP addresses to instances and/or services.

BACKGROUND

In order to communicate via the Internet, network devices are assignedInternet Protocol (IP) addresses. IP addresses are used to identifydevices when sending and receiving traffic via the network.

Configuring network devices, such as server computers, with IP addressesis typically performed by a network administrator. However, manuallyconfiguring and maintaining IP address assignments can be time consumingand error prone. For example, a network administrator may have tomanually manage a list of available IP addresses and manually maintain asufficient number of IP addresses in the list for future assignments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example environment supporting automatedallocation of IP addresses within a region.

FIG. 2 is a diagram of an example environment supporting automatedallocation of IP addresses to available IP address pools and to customerinstances and services.

FIG. 3 is a diagram of an example environment supporting automatedallocation of IP addresses from a global spare IP address pool.

FIG. 4 is a flowchart of an example method for performing automatedallocation of IP addresses within a region.

FIG. 5 is a flowchart of an example method for performing automatedallocation of IP addresses from a common spare IP address pool.

FIG. 6 is a flowchart of an example method for performing automatedallocation of IP addresses from a global spare IP address pool.

FIG. 7 is an example system diagram showing a plurality of virtualmachine instances running in a multi-tenant environment.

FIG. 8 depicts a generalized example of a suitable computing environmentin which the described innovations may be implemented.

DETAILED DESCRIPTION Overview

The following description is directed to techniques and solutions forperforming automated allocation of Internet Protocol (IP) addresses tozones of a service provider environment. From there, the IP addressescan be further allocated to customer instances. A service provider mayoperate a service (e.g., a compute service, storage service, etc.) inmultiple locations world-wide called zones. As described in more detail,zones can have some level of isolation from other zones and, in someembodiments, zones can be completely independent from each other interms of power, networking, and other computing resources. For example,automated allocation of IP addresses can be performed by determiningthat remaining IP addresses in an available IP address pool (e.g., acustomer-available IP address pool for a zone of the service providerenvironment) are below a threshold value, obtaining a range ofcontiguous IP addresses from a common spare IP address pool of theservice provider, and allocating the range of contiguous IP addressesfrom the common spare IP address pool to the available IP address pool.The available IP address pool can then be used to allocate IP addressesto instances (e.g., virtual machine instances running within a cloudcomputing environment, which can also be called customer instances)and/or services.

In some implementations, a common spare IP address pool is used forallocating ranges of contiguous IP addresses within a geographicalregion of the service provider. For example, a geographical region ofcomputing devices can be a collection of computer servers in a datacenter at a particular location (e.g., a city). The common spare IPaddress pool can provide ranges of contiguous IP addresses to a numberof available IP address pools. In turn, the available IP address poolscan provide IP addresses for allocation to devices and/or services inthe geographical region when needed. For example, when a customerinstance is launched in the geographical region, it can automaticallyobtain an IP address (or a number of IP addresses) from one of theavailable IP address pools in the geographical region.

In some implementations, IP address utilization within a geographicalregion is organized on the basis of zones and use cases. A zonerepresents a logical data center and may be mapped to one or morephysical data centers including server computers on which virtualmachine instances run. A zone may be associated with one or moreavailable IP address pools that provide IP addresses for allocation tothe instances (e.g., customer instances) and/or services associated withthe zone. The available IP address pools associated with a particularzone may be general pools (e.g., providing IP addresses to any type ofrequesting instance or service of the zone) or use case pools. A usecase available IP address pool provides IP addresses for allocation toinstances and/or services associated with a particular use case. Oneexample of a use case is an elastic IP use case. An available IP addresspool associated with the elastic IP use case provides IP addresses forinstances and/or services that use elastic IPs (e.g., IP addresses thatcan be re-assigned to different instances and/or services without beingreleased back to the pool). Another example of a use case is a loadbalancer use cases. An available IP address pool associated with theload balancer use case provides IP addresses for instances and/orservices that utilize a load balancer.

Available IP address pools that are not associated with a particularzone can also be provided. For example, available IP address pools foruse cases can be provided across the zones of a region (e.g., calledcross zone use cases). For example, instances and/or services of thevarious zones of a region can allocate IP addresses for a particular usecase from the cross-zone use case available IP address pool.

The IP addresses that are available for allocation from the common spareIP address pool and the available IP address pools are public IPaddresses that are routable via the Internet. For example, the serviceprovider can obtain a block of contiguous IP addresses (e.g., a /16block of IPv4 addresses, which contains 65,536 individual IP addresses)and add it to the common spare IP address pool serving a particularregion. When available IP address pools for the particular zone runslow, ranges of contiguous IP address can be automatically allocated fromthe common spare IP address pool to the available IP address pools. Forexample, a /24 block of IPv4 addresses, which contains 256 individual IPaddresses, can be automatically allocated from the common spare IPaddress pool to a particular available IP address pool. In someimplementations, IPv6 addresses are used instead of, or in addition to,IPv4 addresses.

In some implementations, a global spare IP address pool provides rangesof contiguous IP addresses to one or more common spare IP address poolsin one or more corresponding geographical regions. For example, when IPaddresses in a particular common spare IP address pool fall below athreshold value, a range of contiguous IP addresses (e.g., a /12 blockof IPv4 addresses) can be automatically allocated from the global spareIP address pool to the particular common spare IP address pool. Forexample, the service provider can maintain a global spare IP addresspool that provides IP addresses for allocation to common spare IPaddress pools located in a number of different geographical regions(e.g., to a number of data centers in different locations).

In some implementations, automated allocation of IP addresses isperformed on the basis of contiguous ranges of IP addresses. Forexample, a contiguous range of IP addresses is allocated from a commonspare IP address pool to an available IP address pool when the availableIP address pool runs low (e.g., below a threshold value of available IPaddresses in the pool). In some implementations, automated allocation ofIP addresses can be performed on the basis of non-contiguous ranges(e.g., collections of IP addresses that are not contiguous and/orindividual IP addresses).

The techniques described herein provide advantages over manual IPmanagement solutions. For example, with manual management of free IPaddresses, an administrator can monitor a free pool and add a new rangeof IP addresses when the pool runs low. While manual management of freeIP addresses can work in some situations, it can be time consuming,inefficient, and error prone. For example, an administrator may have tospend a significant amount of time checking free pools and adding new IPaddresses when needed. If the administrator does not check a poolregularly, a pool may run out of available IP addresses, which canresult in service disruption. In addition, an administrator may assign alarge number of IP addresses to a particular pool in order to avoidhaving to check the pool frequently. However, assigning a large numberof IP addresses to a particular pool can result in inefficient use of IPaddresses if a large number sit in the pool unused for a long period oftime.

Using the automated IP allocation techniques described herein, IPaddresses can be managed and utilized efficiently. For example, rangesof IP addresses can be added to pools only when they are needed (e.g.,determined automatically based on a threshold value, which can betailored to the IP usage rate within the particular pool). In addition,the size of a range of IP addresses to be added to a particular pool canbe automatically determined (e.g., based on the IP usage rate within theparticular pool) to maintain efficient utilization of IP addresses.Furthermore, by automatically allocating ranges of contiguous IPaddresses, fragmentation of IP addresses is reduced (e.g., savingcomputing resources by reducing routing complexity and reducing memoryusage by not needing to store routing details for fragmented IPaddresses).

Environments for Automated Allocation of IP Addresses

In any of the implementations described herein, automated allocation ofIP addresses can be performed within computing environments, such asdata centers. For example, ranges of contiguous IP addresses can beautomatically allocated to various available IP address pools within theenvironment. Customer instances and/or services can then beautomatically allocated IP addresses from the various available IPaddress pools when needed (e.g., upon instance and/or service start-up).

FIG. 1 is a diagram of an example environment 100 supporting automatedallocation of IP addresses within a region 110. For example, the region110 can include one or more data centers located in a particulargeographic area, logically mapped to one or more zones. The data centerscan include a collection of computing devices. The region 110 isconnected to the Internet via a network connection (not depicted).Similarly, the zones can be interconnected via one or more privatededicated network links.

A common spare IP address pool 120 is associated with the region 110(e.g., it is operated in a zone within the region). The common spare IPaddress pool 120 maintains a store of free IP addresses for allocationto the various sub-pools of the region 110. Specifically, in the exampleenvironment 100, the common spare IP address pool 120 provides IPaddresses to zone pools (e.g., available IP address pools 152 and 162)and cross-zone pools (e.g., available IP address pools 140).

The region 110 includes a number of zones, including zone 150 and zone160. Each zone is associated with one or more available IP address pools(e.g., customer-available IP address pools). For example zone 150 isassociated with available IP address pools 152. The available IP addresspools 152 can include one or more general pools for the zone 150 and/orone or more use case pools for the zone 150.

Customer instances 154 running within the zone 150 can obtain IPaddresses (e.g., upon instance launch and/or at other times) from theavailable IP address pools 152 and/or from the available IP addresspools for cross-zone use cases 140, as depicted at 170. For example, aparticular customer instance can obtain an IP address from a generalavailable IP address pool (one of the available IP address pools 152 forthe zone 150) upon start-up. As another example, a particular customerinstance can obtain an IP address for a particular use case (e.g., anelastic IP address) from an available IP address pool providing IPaddresses for the elastic IP use case (one of the available IP addresspools for cross-zone use cases 140).

Zone 160 is associated with available IP address pools 162. Theavailable IP address pools 162 can include one or more general pools forthe zone 160 and/or one or more use case pools for the zone 160.Customer instances 164 running within the zone 160 can obtain IPaddresses (e.g., upon instance launch and/or at other times) from theavailable IP address pools 162 and/or from the available IP addresspools for cross-zone use cases 140, as depicted at 170. While two zonesare depicted within the region 110, a region may include any number ofzones.

The available IP address pools associated with zones (e.g., available IPaddress pools 152 and 162) and cross-zone pools (e.g., available IPaddress pools 140) are also called customer-available IP address poolsbecause they hold IP addresses that are available for allocation tocustomer instances (e.g., customer instances 154 and 164). In someimplementations, the customer-available IP address pools provide IPaddresses for allocation to services as well.

Automated allocation of IP addresses can be managed within a region byan IP allocation service. As depicted in the example environment 100, anIP allocation service 130 performs automated allocation of IP addresseswithin the region 110. As depicted at 132, the IP allocation service 130performs operations for automatic IP allocation from the common spare IPaddress pool 120 to the available IP address pools for cross-zone usecases 140 and to the available IP address pools for the zones (availableIP address pools 152 and 162).

For example, the IP allocation service 130 can monitor the available IPaddress pools for cross-zone use cases 140 and the available IP addresspools 152 and 162. When one of the pools becomes low on IP addresses(e.g., when IP addresses in the pool fall below a threshold value), theIP allocation service 130 can obtain a range of contiguous IP addressesfrom the common spare IP address pool 120 and add it to the pool that isrunning low. For example, the IP allocation service 130 can obtain a /24contiguous range of IP addresses and allocate the /24 contiguous rangeof IP addresses to one of the available IP address pools for cross-zoneuse cases 140.

FIG. 2 is a diagram of an example environment 200 supporting automatedallocation of IP addresses to available IP address pools and to customerinstances and services. For example, the environment 200 can represent acollection of computing systems of a business or organization (e.g., oneor more data centers or other groupings of computing systems). Theenvironment 200 can also represent a geographical region.

A common spare IP address pool 220 maintains a store of free IPaddresses for allocation to the various sub-pools of the environment200. In the arrangement depicted in the environment 200, the commonspare IP address pool 220 provides IP addresses to available IP addresspools 240, 242, and 244. The available IP address pools in turn provideIP addresses to customer instances 250 and/or services 260, as depictedat 270. While three available IP address pools are depicted, the exampleenvironment 200 supports any number of available IP address pools.

Automated allocation of IP addresses can be managed within the exampleenvironment 200 by an IP allocation service 230. The IP allocationservice 230 performs automated allocation of IP addresses within theexample environment 200. As depicted at 232, the IP allocation service230 performs operations for automatic IP allocation from the commonspare IP address pool 220 to the available IP address pools 240, 242,and 244. The IP allocation service 230 can be implemented in softwareand/or hardware of one or more computing devices of the exampleenvironment 200.

For example, the IP allocation service 230 can monitor the available IPaddress pools 240, 242, and 244. When one of the available IP addresspools becomes low on IP addresses (e.g., when IP addresses in one of theavailable IP address pools fall below a threshold value), the IPallocation service 230 can obtain a range of contiguous IP addressesfrom the common spare IP address pool 220 and add it to the available IPaddress pool that is running low. For example, the IP allocation service230 can obtain a /24 contiguous range of IP addresses and allocate the/24 contiguous range of IP addresses to one of the available IP addresspools (e.g., to pool 240, 242, or 244).

The available IP address pools 240, 242, and 244 can provide general IPaddresses and/or use case IP addresses to customer instances 240 and/orservices 250. For example, one or more of the available IP address poolscan provide general purpose IP addresses while one or more other of theavailable IP address pools can provide IP addresses for specific usecases. In some implementations, the available IP address pools 240, 242,and 244, the customer instances 250, and the services 260 are dividedinto zones.

FIG. 3 is a diagram of an example environment 300 supporting automatedallocation of IP addresses from a global spare IP address pool toregional common spare IP address pools, and from regional common spareIP address pools to available IP address pools within a given region.The example environment 300 can represent a business or organizationthat maintains computing devices in various locations (e.g., datacenters in different locations). In some implementations, the exampleenvironment 300 represents a cloud computing service provider thatmaintains data centers providing cloud computing services in differentgeographical regions.

As depicted in the example environment 300, a global spare IP addresspool 310 maintains a store of free IP addresses for allocation to commonspare IP address pools located in various regions, including commonspare IP address pool 360 in region 320 and common spare IP address pool365 in region 330. While two regions are depicted (320 and 330), anynumber of regions can be supported within the example environment 300.

The common spare IP address pools maintain stores of free IP addressesfor allocation to the various sub-pools in their respective regions. Forexample, within region 320 common spare IP address pool 360 provides IPaddresses to one or more available IP address pools 370 and withinregion 330 common spare IP address pool 365 provides IP addresses to oneor more available IP address pools 375.

The available IP address pools in turn provide IP addresses to customerinstances and/or services in their respective regions. For example,within region 320 available IP address pools 370 provide IP addressesfor allocation to customer instances and or services 380, and withinregion 330 available IP address pools 375 provide IP addresses forallocation to customer instances and or services 385.

Automated allocation of IP addresses can be managed within the exampleenvironment by various services, including a prefix assignment service305 that manages allocation of IP addresses from the global spare IPaddress pool 310 to the common spare IP address pools in the variousregions (e.g., regions 320 and 330), as depicted at 307. For example,the prefix assignment service 305 can initiate a procedure foradvertising a route to the Internet to direct a range of IP addressesthat is being allocated from the global spare IP address pool 310 to aparticular common spare IP address pool (e.g., to common spare IPaddress pool 360 in region 320).

The prefix assignment service 305 performs or initiates a number ofrouting-related operations when allocating IP addresses from the globalspare IP address pool 310 to a common spare IP address pool in a region.The routing-related operations can include updating border gatewayprotocol (BGP) routes so that the prefix (the network address portion ofthe range of IP addresses being allocated) is advertised out of thecorrect region (the region to which the IP addresses are beingallocated). The routing-related operations can include registering theprefix with geo-location services (e.g., with one or more IPgeo-location services or databases). The routing-related operations caninclude registering the prefix with the appropriate oversight authority(e.g., the American Registry for Internet Numbers (ARIN) for NorthAmerica). The routing-related operations can include updating domainname system (DNS) records. The routing-related operations can alsoinclude notifying customers that a new prefix has been added to aparticular region (e.g., so that customers can update white lists and/orblack lists).

As depicted, an IP allocation service within each region performsautomated allocation of IP addresses within its respective region.Specifically, IP allocation service 340 performs automated allocation ofIP addresses within region 320. As depicted at 350, IP allocationservice 340 performs operations for automatic IP allocation from thecommon spare IP address pool 360 to the available IP address pools 370(e.g., when the number of free IP addresses in one of the available IPaddress pools 370 falls below a threshold value). The IP allocationservice 340 can also perform operations for automatically assigning IPaddresses from the available IP address pools 370 to the customerinstances and/or services 380, and for handling IP addresses that arereleased from the customer instances and/or services 380. The IPallocation service 340 can also participate in automatic IP allocationfrom the global spare IP address pool 310 to the common spare IP addresspool 360 (e.g., when the number of free IP addresses in the common spareIP address pool 360 falls below a threshold value). For example, the IPallocation service 340 can receive a range of contiguous IP addressesfrom the prefix assignment service 305 and add it to the common spare IPaddress pool 360. The IP allocation services for other regions performthese operations for their respective regions (e.g., IP allocationservice 345 performs automated allocation of IP addresses within region330, including the operations depicted at 355).

In some implementations, no Internet routing changes are needed whenautomatically allocating ranges of contiguous IP addresses to availableIP address pools (e.g., to customer-available IP address pools). Forexample, IP addresses stored within a common spare IP address pool canbe routed via the Internet to a specific geographical region of abusiness or organization (e.g., a specific data center or other group ofcomputing systems). When a range of contiguous IP addresses is allocatedfrom the common spare IP address pool to an available IP address poolwithin the geographical region, Internet routing can remain the same(e.g., routes to the range of contiguous IP addresses can still directtraffic to the geographical region). However, depending on networkingdetails of the region, internal or local routing may need to be adjusted(e.g., local routing managed by the business or organization within theregion).

In some implementations, Internet routing changes are needed whenautomatically allocating contiguous ranges of IP addresses from a globalspare IP address pool to a common spare IP address pool. For example,when a range of contiguous IP addresses is allocated from the globalspare IP address pool to a common spare IP address pool in a particulargeographical region, Internet routing may need to be changed to directnetwork traffic for the range of contiguous IP addresses to theparticular geographical region.

In some implementations, customer instances and/or services obtainsingle IP addresses from an available IP address pool. In someimplementations, customer instances and/or services can also obtain ablock of IP addresses (e.g., a contiguous block, such as 8 or 16 IPaddresses) from an available IP address pool. In some implementations,IP addresses in an available IP address pool are segmented into at leasta first group from which individual IP addresses are allocated tocustomer instances and/or services and a second group from which blocksof contiguous IP addresses are allocated to customer instances and/orservices. By maintaining two separate groups (one for individual IPs andone for blocks of IPs), fragmentation can be reduced. For example,blocks of contiguous IPs can be allocated from a specific group of IPsin an available IP address pool and released back to the same groupwithout being fragmented.

Automated Allocation of IP Addresses

In any of the implementations described herein, ranges of contiguous IPaddresses can be automatically added to a pool of IP addresses (e.g., acustomer-available IP address pool, an available IP address pool, and/orother types of pools that store free IP addresses) when the pool runslow. In order to determine when to automatically add a range ofcontiguous IP addresses to a pool, a threshold value can be determined.When available IP addresses in the pool fall below the threshold value,another range of contiguous IP addresses can be added.

In some implementations, the threshold value for a particular pool isdetermined based at least in part on a historical allocation rate fromthe pool and a historical release rate back to the pool. The historicalallocation rate for IP addresses from the pool (e.g., an available IPaddress pool) indicates the rate at which IP addresses are allocatedfrom the pool (e.g., the number of IP addresses that are assigned tocustomer instances and/or services per day). The historical release ratefor IP addresses back to the pool (e.g., an available IP address pool)indicates the rate at which IP addresses are released and added back tothe pool (e.g., the number of IP addresses that are released by customerinstances and/or services and returned to the pool per day). Thehistorical rates can be determined by monitoring (e.g., by an IPallocation service) allocation and release rates over a period of time,such as a week or month.

Depending at least in part on the historical allocation rate and thehistorical release rate for a particular pool, a threshold value can bedetermined. For example, if the historical allocation rate for aparticular pool is large compared to the historical release rate, thenthe threshold value can be set relatively high to ensure that enough IPaddresses will be available in the pool to satisfy the relatively largedemand for a period of time. However, if the historical allocation ratefor a particular pool is only slightly higher than the historicalrelease rate, then the threshold value can be set relatively low.

In some implementations, released IP addresses are not added back to apool (e.g., to an available IP address pool) for an amount of timespecified by a no-reuse window value. For example, if the no-reusewindow value is set to 24 hours, then an IP address that is released(e.g., by a customer instance or a service) will not be available forallocation to another customer instance or another service for 24 hours(e.g., the released IP address is not added back to the available IPaddress pool). In some implementations, the no-reuse window provides anopportunity for the customer or service to reclaim the released IPaddress during the no-reuse window time period (e.g., the IP address mayhave been mistakenly released by a customer operating a virtual machineinstance). Implementing a no-reuse window can protect a customer fromothers whose use (intentional or unintentional) of the released IPaddress could reflect negatively on the customer. For example, ifsomeone obtains the released IP address and implements a denial ofservice attack, such an attack could be attributed to the customer if asufficient amount of time has not elapsed since the IP address wasreleased.

In some implementations, the threshold value for a particular pool isautomatically determined such that the pool has sufficient IP addressesto last a specific amount of time (e.g., pre-determined number of days).For example, if IP addresses are being allocated from the pool at a rateof 1,000 per day and released to the pool at a rate of 500 per day, anda setting for the pool indicates that the pool should have 5 days ofavailable IP addresses, then the threshold value can be set to 2,500 IPaddresses.

In some implementations, the threshold value that is determined for aparticular pool represents a number of days of coverage for the pool(i.e., a number of free IP addresses in the pool that is expected tolast for the number of days if no new IP addresses are added to thepool) based on the specific allocation rate and release rate for theparticular pool. For example, the number of days of coverage could be 10days. In a specific implementation, the threshold value is calculatedusing the following equation (Equation 1):Number of free IPs in pool=(allocation rate−release rate)*desiredcoverageAccording to Equation 1, the threshold value specifies a minimum numberof free IPs in the pool and is calculated based on the differencebetween the historical allocation rate and the historical release ratefor the pool multiplied by the number of days of desired coverage. Forexample, if the historical allocation rate is 1,000 IPs/day and thehistorical release rate is 500 IPs/day and the desired coverage is 10days, then the threshold value would be 5,000 IPs.

In some implementations, Equation 1 above is modified to include abuffer period. The buffer period operates to increase the number of freeIPs in the pool to by taking the no-reuse window into account. In aspecific implementation, the threshold value is calculated using thefollowing equation (Equation 2):Number of free IPs in pool=(allocation rate−release rate)*desiredcoverage+releases rate*no-reuse window

According to Equation 2, the value calculated in Equation 1 above isincreased by the historical release rate multiplied by the no-reusewindow (in days). For example, if the historical allocation rate is1,000 IPs/day, the historical release rate is 500 IPs/day, the desiredcoverage is 10 days, and the no-reuse window is 1 day (24 hours), thenthe threshold value would be 5,500 IPs.

In some implementations, the threshold value can be increased to takeinto account allocation spikes. For example, if a particular poolexperiences large spikes (e.g., days in which the allocation rate is tentimes the average allocation rate), then the threshold value can beincreased. In some implementations, the threshold value is increased byincreasing the desired coverage (e.g., from 10 days to 15 days). Inother implementations, the threshold value is increased by a spikeamount. For example, Equation 1 or Equation 2 above can be modified byadding the highest allocation day in the past month (or other historicaltime period).

In some implementations, the rate of IP address utilization is used todetermine IP address allocation size. For example, if the allocationrate (e.g., the ratio or difference between the historical allocationrate and the historical release rate) for a particular pool is high,then a larger range of contiguous IP addresses can be allocated when thepool falls below the threshold value (e.g., a /22 range of IPv4addresses may be allocated to an available IP address pool instead of a/24 range of IPv4 addresses). On the other hand, if the allocation ratefor a particular pool is low, then a smaller range of contiguous IPaddresses can be allocated when the pool falls below the thresholdvalue.

Methods for Automated Allocation of IP Addresses

In any of the technologies described herein, methods can be provided forautomated allocation of IP addresses. For example, automated allocationof IP addresses can be provided within a geographical region.

FIG. 4 is a flow chart of an example method 400 for performing automatedallocation of IP addresses within a region. The IP addresses allocatedby the example method 400 are public IP addresses that are routable viathe Internet. The example method 400 can be performed by an IPallocation service, such as IP allocation service 130 running withinregion 110.

At 410, it is determined that remaining IP addresses in acustomer-available IP address pool are below a threshold value. Theremaining IP addresses in a customer-available IP address pool are theIP addresses that are available in the IP address pool for allocation(e.g., IP addresses that are currently unused and therefore availablefor allocation to customer instances). In order to make thedetermination, the customer-available IP address pool can be monitoredperiodically (e.g., very five minutes, every hour, or every day) orchecked upon the occurrence of a particular event (e.g., checked when anIP address is allocated from the customer-available IP address pool to acustomer instance). The customer-available IP address pool can bemonitored or checked by an IP allocation service. The customer-availableIP address pool provides IP addresses to customer instances (also calledcustomer virtual machine instances).

Upon determining that remaining IP addresses in the customer-availableIP address pool are below the threshold value, the operations depictedat 420 and 430 are performed. Specifically, at 420, a range ofcontiguous IP addresses are obtained from a common spare IP addresspool. For example, range of contiguous IP addresses could be a /24 rangeof IP addresses.

At 430, the range of contiguous IP addresses (obtained at 420) isallocated to the customer-available IP address pool. For example, the/24 range of IP addresses can be added to the customer-available IPaddress pool.

As indicated at 440, the common spare IP address pool is used forautomated allocation of ranges of contiguous IP addresses within ageographical region of computing devices. In addition, the examplemethod 400 can be used to automatically allocate contiguous IP rangesfrom the common spare IP address pool to a plurality ofcustomer-available IP address pools, including the customer-available IPaddress pool.

FIG. 5 is a flow chart of an example method 500 for performing automatedallocation of IP addresses from a common spare IP address pool. Forexample, the example method 500 can be performed by an IP allocationservice, such as IP allocation service 230. The IP addresses allocatedby the example method 500 are public IP addresses that are routable viathe Internet.

At 510, it is determined that remaining IP addresses in an available IPaddress pool are below a threshold value. The remaining IP addresses inan available IP address pool are the IP addresses that are currentlyavailable in the available IP address pool for allocation (e.g., IPaddresses that are currently unused and therefore available forallocation to customer instances or services). In order to make thedetermination, the available IP address pool can be monitoredperiodically (e.g., very five minutes, every hour, or every day) orchecked upon the occurrence of a particular event (e.g., checked when anIP address is allocated from the available IP address pool to a customerinstance or a service). The available IP address pool can be monitoredor checked by an IP allocation service. The available IP address poolprovides IP addresses to devices and/or services. For example, theavailable IP address pool can provide IP addresses for assignment tocustomer instances (also called customer virtual machine instances)and/or other types of computing services (e.g., networking services).

Upon determining that remaining IP addresses in the available IP addresspool are below the threshold value, the operations depicted at 520 and530 are performed. Specifically, at 520, a range of contiguous IPaddresses is obtained from a common spare IP address pool. For example,the range of contiguous IP addresses could be a /24 range of IPaddresses.

At 530, the range of contiguous IP addresses (obtained at 520) isallocated to the available IP address pool. For example, the /24 rangeof IP addresses can be added to the available IP address pool.

The example method 500 can be used to automatically allocate ranges ofcontiguous IP addresses from the common spare IP address pool to anumber of available IP address pools (e.g., available address poolsassociated with particular zones and/or use cases). The example method500 can automatically allocate ranges of contiguous IP addresses among acollection of computing devices, such as a collection of computingdevices located at a particular data center.

FIG. 6 is a flow chart of an example method 600 for performing automatedallocation of IP addresses from a global spare IP address pool. The IPaddresses allocated by the example method 600 are public IP addressesthat are routable via the Internet. For example, the example method 600can be performed by various services that manage automated allocation ofIP addresses, such as prefix assignment service 305 and IP allocationservices 340 and 345.

At 610, it is determined that remaining IP addresses in a common spareIP address pool are below a first threshold value. The remaining IPaddresses in a common spare IP address pool are the IP addresses thatare currently available in the common spare IP address pool forallocation (e.g., IP addresses that are currently unused and thereforeavailable for allocation to available IP address pools). In order tomake the determination, the common spare IP address pool can bemonitored periodically (e.g., very five minutes, every hour, or everyday) or checked upon the occurrence of a particular event (e.g., checkedwhen ranges of IP addresses are allocated to sub-pools). The commonspare IP address pool can be monitored or checked by an IP allocationservice.

At 620, in response to determining that the remaining IP addresses inthe common spare IP address pool are below the first threshold value, arange of contiguous IP addresses are allocated from a global spare IPaddress pool to the common spare IP address pool.

At 630, a routing update is initiated to directing traffic for the rangeof contiguous IP addresses to a location (e.g., a region) associatedwith the common spare IP address pool. For example, the routing updatecan comprise one or more routing-related operations, such as updates toBGP routes, registration with geo-location services, registration withoversight authorities, DNS updates, and/or notifications to customers.The routing update can be initiated by a service, such as the prefixassignment service 305.

At 640, it is determined that remaining IP addresses in an available IPaddress pool are below a second threshold value. The remaining IPaddresses in an available IP address pool are the IP addresses that arecurrently available in the available IP address pool for allocation(e.g., IP addresses that are currently unused and therefore availablefor allocation to customer instances or services). In order to make thedetermination, the available IP address pool can be monitoredperiodically (e.g., very five minutes, every hour, or every day) orchecked upon the occurrence of a particular event (e.g., checked when anIP address is allocated from the available IP address pool to a customerinstance or a service). The available IP address pool can be monitoredor checked by the IP allocation service. The available IP address poolprovides IP addresses to devices and/or services. For example, theavailable IP address pool can provide IP addresses for assignment tocustomer instances (also called customer virtual machine instances)and/or other types of computing services (e.g., networking services).

In response to determining that remaining IP addresses in the availableIP address pool are below the second threshold value, the operationsdepicted at 650 and 660 are performed. Specifically, at 650, a range ofcontiguous IP addresses is obtained from the common spare IP addresspool. For example, a range of contiguous IP addresses could be a /24range of IP addresses.

At 660, the range of contiguous IP addresses (obtained at 650) isallocated to the available IP address pool. For example, the /24 rangeof IP addresses can be added to the available IP address pool.

The example method 600 can be used to automatically allocate ranges ofcontiguous IP addresses from the global spare IP address pool to anumber of common spare IP address pools (e.g., where each of the commonspare IP address pool serves a collection of computing devices, such asa data center or region). Each common spare IP address pool can thenprovide IP addresses for automatic allocation to its associatedavailable IP address pools.

In the example method 600, the first threshold value can beautomatically calculated from usage statistics of the common spare IPaddress pool (e.g., historical allocation and release rates for thecommon spare IP address pool). The second threshold value can beautomatically calculated from usage statistics of the available IPaddress pool (e.g., historical allocation and release rates for theavailable spare IP address pool).

Example Service Provider Environments

FIG. 7 is a computing system diagram of a network-based compute serviceprovider 700 that illustrates one environment in which embodimentsdescribed herein can be used. By way of background, the compute serviceprovider 700 (i.e., the cloud provider) is capable of delivery ofcomputing and storage capacity as a service to a community of endrecipients. In an example embodiment, the compute service provider canbe established for an organization by or on behalf of the organization.That is, the compute service provider 700 may offer a “private cloudenvironment.” In another embodiment, the compute service provider 700supports a multi-tenant environment, wherein a plurality of customersoperate independently (i.e., a public cloud environment). Generallyspeaking, the compute service provider 700 can provide the followingmodels: Infrastructure as a Service (“IaaS”), Platform as a Service(“PaaS”), and/or Software as a Service (“SaaS”). Other models can beprovided. For the IaaS model, the compute service provider 700 can offercomputers as physical or virtual machines and other resources. Thevirtual machines can be run as guests by a hypervisor, as describedfurther below. The PaaS model delivers a computing platform that caninclude an operating system, programming language execution environment,database, and web server. Application developers can develop and runtheir software solutions on the compute service provider platformwithout the cost of buying and managing the underlying hardware andsoftware. The SaaS model allows installation and operation ofapplication software in the compute service provider. In someembodiments, end users access the compute service provider 700 usingnetworked client devices, such as desktop computers, laptops, tablets,smartphones, etc. running web browsers or other lightweight clientapplications. Those skilled in the art will recognize that the computeservice provider 700 can be described as a “cloud” environment.

The particular illustrated compute service provider 700 includes aplurality of server computers 702A-702D. While only four servercomputers are shown, any number can be used, and large centers caninclude thousands of server computers. The server computers 702A-702Dcan provide computing resources for executing software instances706A-706D. In one embodiment, the instances 706A-706D are virtualmachines. As known in the art, a virtual machine is an instance of asoftware implementation of a machine (i.e. a computer) that executesapplications like a physical machine. In the example, each of theservers 702A-702D can be configured to execute a hypervisor 708 oranother type of program configured to enable the execution of multipleinstances 706 on a single server. For example, each of the servers702A-702D can be configured (e.g., via the hypervisor 708) to supportone or more virtual machine slots, with each virtual machine slotcapable of running a virtual machine instance (e.g., server computer702A could be configured to support three virtual machine slots eachrunning a corresponding virtual machine instance). Additionally, each ofthe instances 706 can be configured to execute one or more applications.

It should be appreciated that although the embodiments disclosed hereinare described primarily in the context of virtual machines, other typesof instances can be utilized with the concepts and technologiesdisclosed herein. For instance, the technologies disclosed herein can beutilized with storage resources, data communications resources, and withother types of computing resources. The embodiments disclosed hereinmight also execute all or a portion of an application directly on acomputer system without utilizing virtual machine instances.

One or more server computers 704 can be reserved for executing softwarecomponents for managing the operation of the server computers 702 andthe instances 706. For example, the server computer 704 can execute amanagement component 710. A customer can access the management component710 to configure various aspects of the operation of the instances 706purchased by the customer. For example, the customer can purchase, rentor lease instances and make changes to the configuration of theinstances. The customer can also specify settings regarding how thepurchased instances are to be scaled in response to demand. Themanagement component can further include a policy document to implementcustomer policies. An auto scaling component 712 can scale the instances706 based upon rules defined by the customer. In one embodiment, theauto scaling component 712 allows a customer to specify scale-up rulesfor use in determining when new instances should be instantiated andscale-down rules for use in determining when existing instances shouldbe terminated. The auto scaling component 712 can consist of a number ofsubcomponents executing on different server computers 702 or othercomputing devices. The auto scaling component 712 can monitor availablecomputing resources over an internal management network and modifyresources available based on need.

A deployment component 714 can be used to assist customers in thedeployment of new instances 706 of computing resources. The deploymentcomponent can have access to account information associated with theinstances, such as who is the owner of the account, credit cardinformation, country of the owner, etc. The deployment component 714 canreceive a configuration from a customer that includes data describinghow new instances 706 should be configured. For example, theconfiguration can specify one or more applications to be installed innew instances 706, provide scripts and/or other types of code to beexecuted for configuring new instances 706, provide cache logicspecifying how an application cache should be prepared, and other typesof information. The deployment component 714 can utilize thecustomer-provided configuration and cache logic to configure, prime, andlaunch new instances 706. The configuration, cache logic, and otherinformation may be specified by a customer using the managementcomponent 710 or by providing this information directly to thedeployment component 714. The instance manager can be considered part ofthe deployment component.

Customer account information 715 can include any desired informationassociated with a customer of the multi-tenant environment. For example,the customer account information can include a unique identifier for acustomer, a customer address, billing information, licensinginformation, customization parameters for launching instances,scheduling information, auto-scaling parameters, previous IP addressesused to access the account, etc.

A network 730 can be utilized to interconnect the server computers702A-702D and the server computer 704. The network 730 can be a localarea network (LAN) and can be connected to a Wide Area Network (WAN) 740so that end users can access the compute service provider 700. It shouldbe appreciated that the network topology illustrated in FIG. 7 has beensimplified and that many more networks and networking devices can beutilized to interconnect the various computing systems disclosed herein.

In some implementations, an IP allocation service 716 provides forautomated allocation of IP addresses within the local area network 730.For example, the IP allocation service 716 can manage IP address pools717 (including a common spare IP address pool and available addresspools). For example, the IP allocation service 716 can allocate rangesof contiguous IP addresses from the common spare IP address pool to theavailable IP address pools when available IP addresses fall below athreshold amount. The IP allocation service 716 can also receiverequests from the various devices and services of the local area network730 and provide IP addresses from the available IP address pools. Forexample, the IP allocation service 716 can receive a request when a newcustomer instance launches (e.g., one of the instances 706A) and providean IP address form one of the available IP address pools in response forthe new customer instance to use. The IP allocation service 716 can alsoreceive IP addresses that have been released by customer instances(e.g., upon instance shutdown) and return them to an available IPaddress pool (e.g., after a no-reuse window time period has expired).

FIG. 8 depicts a generalized example of a suitable computing environment800 in which the described innovations may be implemented. The computingenvironment 800 is not intended to suggest any limitation as to scope ofuse or functionality, as the innovations may be implemented in diversegeneral-purpose or special-purpose computing systems. For example, thecomputing environment 800 can be any of a variety of computing devices(e.g., desktop computer, laptop computer, server computer, tabletcomputer, etc.)

With reference to FIG. 8, the computing environment 800 includes one ormore processing units 810, 815 and memory 820, 825. In FIG. 8, thisbasic configuration 830 is included within a dashed line. The processingunits 810, 815 execute computer-executable instructions. A processingunit can be a general-purpose central processing unit (CPU), processorin an application-specific integrated circuit (ASIC) or any other typeof processor. In a multi-processing system, multiple processing unitsexecute computer-executable instructions to increase processing power.For example, FIG. 8 shows a central processing unit 810 as well as agraphics processing unit or co-processing unit 815. The tangible memory820, 825 may be volatile memory (e.g., registers, cache, RAM),non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or somecombination of the two, accessible by the processing unit(s). The memory820, 825 stores software 880 implementing one or more innovationsdescribed herein, in the form of computer-executable instructionssuitable for execution by the processing unit(s).

A computing system may have additional features. For example, thecomputing environment 800 includes storage 840, one or more inputdevices 850, one or more output devices 860, and one or morecommunication connections 870. An interconnection mechanism (not shown)such as a bus, controller, or network interconnects the components ofthe computing environment 800. Typically, operating system software (notshown) provides an operating environment for other software executing inthe computing environment 800, and coordinates activities of thecomponents of the computing environment 800.

The tangible storage 840 may be removable or non-removable, and includesmagnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any othermedium which can be used to store information in a non-transitory wayand which can be accessed within the computing environment 800. Thestorage 840 stores instructions for the software 880 implementing one ormore innovations described herein.

The input device(s) 850 may be a touch input device such as a keyboard,mouse, pen, or trackball, a voice input device, a scanning device, oranother device that provides input to the computing environment 800. Theoutput device(s) 860 may be a display, printer, speaker, CD-writer, oranother device that provides output from the computing environment 800.

The communication connection(s) 870 enable communication over acommunication medium to another computing entity. The communicationmedium conveys information such as computer-executable instructions,audio or video input or output, or other data in a modulated datasignal. A modulated data signal is a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia can use an electrical, optical, RF, or other carrier.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed methods can be used in conjunction with other methods.

Any of the disclosed methods can be implemented as computer-executableinstructions stored on one or more computer-readable storage media(e.g., one or more optical media discs, volatile memory components (suchas DRAM or SRAM), or non-volatile memory components (such as flashmemory or hard drives)) and executed on a computer (e.g., anycommercially available computer, including smart phones or other mobiledevices that include computing hardware). The term computer-readablestorage media does not include signals and carrier waves, and does notinclude communication connections. Any of the computer-executableinstructions for implementing the disclosed techniques as well as anydata created and used during implementation of the disclosed embodimentscan be stored on one or more computer-readable storage media. Thecomputer-executable instructions can be part of, for example, adedicated software application or a software application that isaccessed or downloaded via a web browser or other software application(such as a remote computing application). Such software can be executed,for example, on a single local computer (e.g., any suitable commerciallyavailable computer) or in a network environment (e.g., via the Internet,a wide-area network, a local-area network, a client-server network (suchas a cloud computing network), or other such network) using one or morenetwork computers.

For clarity, only certain selected aspects of the software-basedimplementations are described. Other details that are well known in theart are omitted. For example, it should be understood that the disclosedtechnology is not limited to any specific computer language or program.For instance, the disclosed technology can be implemented by softwarewritten in C++, Java, Perl, JavaScript, Adobe Flash, or any othersuitable programming language. Likewise, the disclosed technology is notlimited to any particular computer or type of hardware. Certain detailsof suitable computers and hardware are well known and need not be setforth in detail in this disclosure.

It should also be well understood that any functionality describedherein can be performed, at least in part, by one or more hardware logiccomponents, instead of software. For example, and without limitation,illustrative types of hardware logic components that can be used includeField-programmable Gate Arrays (FPGAs), Program-specific IntegratedCircuits (ASICs), Program-specific Standard Products (ASSPs),System-on-a-chip systems (SOCs), Complex Programmable Logic Devices(CPLDs), etc.

Furthermore, any of the software-based embodiments (comprising, forexample, computer-executable instructions for causing a computer toperform any of the disclosed methods) can be uploaded, downloaded, orremotely accessed through a suitable communication means. Such suitablecommunication means include, for example, the Internet, the World WideWeb, an intranet, software applications, cable (including fiber opticcable), magnetic communications, electromagnetic communications(including RF, microwave, and infrared communications), electroniccommunications, or other such communication means.

The disclosed methods, apparatus, and systems should not be construed aslimiting in any way. Instead, the present disclosure is directed towardall novel and nonobvious features and aspects of the various disclosedembodiments, alone and in various combinations and subcombinations withone another. The disclosed methods, apparatus, and systems are notlimited to any specific aspect or feature or combination thereof, nor dothe disclosed embodiments require that any one or more specificadvantages be present or problems be solved.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. Therefore,what is claimed as the invention is all that comes within the scope ofthese claims.

What is claimed is:
 1. A method, implemented by a computing device, forperforming automated allocation of Internet Protocol (IP) addresses, themethod comprising: determining, by the computing device comprising aprocessing unit and memory, that remaining IP addresses which areavailable for allocation in a customer-available IP address pool arebelow a threshold value; and upon determining that the remaining IPaddresses are below the threshold value: obtaining, by the computingdevice from a data store that stores a common spare IP address pool, arange of contiguous IP addresses from the common spare IP address pool;and allocating, by the computing device to a data store that stores thecustomer-available IP address pool, the range of contiguous IP addressesobtained from the common spare IP address pool to the customer-availableIP address pool; wherein the common spare IP address pool is used forautomated allocation of ranges of contiguous IP addresses within ageographical region of computing devices; wherein the common spare IPaddress pool contains public IP addresses that are routable via theInternet; and wherein contiguous IP ranges are automatically allocatedfrom the common spare IP address pool to a plurality ofcustomer-available IP address pools, including the customer-available IPaddress pool, and wherein customer instances obtain IP addresses fromthe customer-available IP address pools.
 2. The method of claim 1wherein the plurality of customer-available IP address pools include oneor more of the following pool types: a customer-available IP addresspool that provides IP addresses for a particular zone; acustomer-available IP address pool that provides IP addresses for aparticular use case within a particular zone; or a customer-available IPaddress pool that provides IP addresses for a particular use case acrossa plurality of zones.
 3. The method of claim 1 wherein the thresholdvalue is determined, at least in part, using: a historical allocationrate for IP addresses from the customer-available IP address pool; and ahistorical release rate for IP addresses back to the customer-availableIP address pool.
 4. The method of claim 1 wherein the determining thatremaining IP addresses in a customer-available IP address pool are belowa threshold value comprises: determining a historical allocation ratefor IP addresses from the customer-available IP address pool;determining a historical release rate for IP addresses back to thecustomer-available IP address pool; obtaining a no-reuse window value;obtaining a desired coverage value; and calculating the threshold valueusing at least the historical allocation rate, the historical releaserate, the no-reuse window value, and the desired coverage value.
 5. Themethod of claim 1 further comprising: receiving one or more IP addressesreleased by a customer instance; obtaining a no-reuse window value; andadding the one or more IP addresses released by the customer instance tothe customer-available IP address pool after a length of time specifiedby the no-reuse window value; wherein the one or more IP addressesreleased by the customer instance are not available for re-allocation toa different customer until the length of time has expired.
 6. The methodof claim 1 further comprising: receiving a request to allocate an IPaddress for a customer instance; obtaining an IP address from thecustomer-available IP address pool; and allocating the obtained IPaddress to the customer instance.
 7. A computing device comprising: oneor more processing units; wherein the computing device is configured toperform operations for automated allocation of Internet Protocol (IP)addresses, the operations comprising: determining that remaining IPaddresses in an available IP address pool are below a threshold value,wherein the threshold value is determined, at least in part, using: ahistorical allocation rate for IP addresses from the available IPaddress pool; and a historical release rate for IP addresses back to theavailable IP address pool; and upon determining that the remaining IPaddresses are below the threshold value: obtaining, from a data storethat stores a common spare IP address pool, a range of contiguous IPaddresses from the common spare IP address pool; and allocating, to adata store that stores the available IP address pool, the range ofcontiguous IP addresses obtained from the common spare IP address poolto the available IP address pool; wherein the common spare IP addresspool is used for automated allocation of ranges of contiguous IPaddresses within a geographical region of computing devices.
 8. Thecomputing device of claim 7 further comprising: receiving a request,from a customer instance or a service, to allocate an IP address fromthe available IP address pool; in response to the request: obtaining anIP address from the available IP address pool; and allocating theobtained IP address to the customer instance or service.
 9. Thecomputing device of claim 7 further comprising: receiving one or more IPaddresses released by a customer instance or a service; obtaining ano-reuse window value; and adding the one or more IP addresses releasedby the customer instance or the service to the available IP address poolafter a length of time specified by the no-reuse window value; whereinthe one or more IP addresses released by the customer instance or theservice are not available for re-allocation to a different customer or adifferent service until the length of time has expired.
 10. Thecomputing device of claim 7 wherein the remaining IP addresses in theavailable IP address pool are segmented into groups comprising: a firstgroup from which customer instances or services allocate individual IPaddresses; and a second group from which customer services or instancesallocation blocks of contiguous IP addresses.
 11. The computing deviceof claim 7 wherein the determining that remaining IP addresses in anavailable IP address pool are below a threshold value further comprises:obtaining a no-reuse window value; obtaining a desired coverage value;and calculating the threshold value using at least the historicalallocation rate, the historical release rate, the no-reuse window value,and the desired coverage value.
 12. The computing device of claim 7wherein contiguous IP ranges are automatically allocated from the commonspare IP address pool to a plurality of available IP address pools,including the available IP address pool, and wherein customer instancesobtain IP addresses from the available IP address pool when needed andrelease IP address back to the available IP address pool when notneeded.
 13. The computing device of claim 12 wherein each available IPaddress pool of the plurality of available IP address pools is of one ofthe following pool types: an available IP address pool that provides IPaddresses for a particular zone; an available IP address pool thatprovides IP addresses for a particular use case within a particularzone; or an available IP address pool that provides IP addresses for aparticular use case across a plurality of zones.
 14. The computingdevice of claim 7 wherein the operations for automated allocation of IPaddresses are performed by an IP allocation service running on thecomputing device that monitors the available IP address pool andallocates ranges of contiguous IP addresses from the common spare IPaddress pool when needed for the geographical region of computingdevices that provide cloud computing services.
 15. A non-transitorycomputer-readable storage medium storing computer-executableinstructions for causing a computing device comprising to perform forperforming automated allocation of Internet Protocol (IP) addresses, theoperations comprising: determining that remaining IP addresses in acommon spare IP address pool are below a first threshold value, whereinthe common spare IP address pool services a region; and upon determiningthat the remaining IP addresses in the common spare IP address pool arebelow the first threshold value, allocating a range of contiguous IPaddresses from a global spare IP address pool to a data store storingthe common spare IP address pool; initiating a routing update todirecting traffic for the range of contiguous IP addresses to the regionserviced by the common spare IP address pool; determining that remainingIP addresses in an available IP address pool are below a secondthreshold value; and upon determining that the remaining IP addresses inthe available IP address pool are below the second threshold value:obtaining a range of contiguous IP addresses from the data store storingthe common spare IP address pool; and allocating the range of contiguousIP addresses obtained from the common spare IP address pool to a datastore storing the available IP address pool.
 16. The computer-readablestorage medium of claim 15, wherein the global spare IP address pool isused for automated allocation of ranges of contiguous IP addresses amonga plurality of common spare IP address pools, including the common spareIP address pool, for a plurality of corresponding regions.
 17. Thecomputer-readable storage medium of claim 16, wherein each region of theplurality of regions contains: the common spare IP address pool for theregion; and a plurality of available IP address pools for the region;wherein customer instances running within the region obtain IP addressesfrom the plurality of available IP address pools for the region.
 18. Thecomputer-readable storage medium of claim 15, further comprising:receiving one or more IP addresses released by a customer instance or aservice; obtaining a no-reuse window value; and adding the one or moreIP addresses released by the customer instance or the service to theavailable IP address pool after a length of time specified by theno-reuse window value; wherein the one or more IP addresses released bythe customer instance or the service are not available for re-allocationto a different customer or a different service until the length of timehas expired.
 19. The computer-readable storage medium of claim 15,wherein the second threshold value is determined, at least in part,using: a historical allocation rate for IP addresses from the availableIP address pool; and a historical release rate for IP addresses back tothe available IP address pool.
 20. The computer-readable storage mediumof claim 15, wherein the determining that remaining IP addresses in anavailable IP address pool are below a second threshold value comprises:determining a historical allocation rate for IP addresses from theavailable IP address pool; determining a historical release rate for IPaddresses back to the available IP address pool; obtaining a no-reusewindow value; obtaining a desired coverage value; and calculating thesecond threshold value using at least the historical allocation rate,the historical release rate, the no-reuse window value, and the desiredcoverage value.